Undelivered Mail Returned to Sender

Undelivered Mail Returned to Sender

My email to one recipient has been blocked as follows:

ERROR_CODE :550, ERROR_CODE :mx5.tb.ukmail.iss.as9143.net bizsmtp Connection rejected. Your IP 135.84.80.237 is in RBL

Received:from mail.zoho.com by mx.zohomail.com
    with SMTP id 1495922992230169.83104677195604; Sat, 27 May 2017 15:09:52 -0700 (PDT)
Message-ID:<15c4bf56463.101 a9f6e65851.2363803582930788365@zoho.com>
Date:Sat, 27 May 2017 23:09:52 +0100
From:Dave Palmer < dave.palmer3@zoho.com>
User-Agent:Zoho Mail

Can you advise?